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Relevant academic research and scientific papers

Asymmetric synthesis of new chiral 1,2- and 1,3-diols

Seven chiral 1,2-diols and six chiral 1,3-diols were synthesized by the asymmetric reduction of the corresponding 1,2-diketones and 1,3-diketones using oxazaborolidine-BH3 catalyst. The 13 corresponding racemic 1,2- and 1,3-diols were synthesized by reducing the diketones with NaBH4 and they were used for determining the ee values through their chiral resolution on HPLC and GC. Five starting diketones, four racemic 1,2-diols, five chiral 1,2-diols, and two chiral 1,3-diols are novel compounds. The new chiral compounds were characterized by IR, 1H and 13C NMR, MS, and elemental analysis. The asymmetric reduction method, oxazaborolidine-BH 3, was applied to these diketones for the first time in this study. The relationship between the structure of the diketone and the yield, diastereoselectivity, and enantiomeric excess was discussed.

REACTIONS IN MICROEMULSION MEDIA. BOROHYDRIDE REDUCTION OF MONO- AND DICARBONYL COMPOUNDS

Microemulsions were prepared at 26 deg C from mixtures of hexanes (O), a 50:1 (w/w) solution (W) of 0.1 M KOH-NaBH4, and a 1.23:1 (w/w) mixture (S) of hexadecyltrimethylammonium bromide (HTABr) and 1-butanol.A pseudoternary phase map contained a significant microemulsion (μE) region, and μE's A and B (60:35:5 and 20:10:70 S:W:O, respectively) were used for reduction of several monocarbonyl compounds , an α,β-unsaturated ketone , and a diketone at 26 deg C.For comparison purposes, reductions were also performed in aqueous 2-propanol (2-PrOH A and 2-PrOH B) prepared by the substitution of 2-propanol for the S and O components of μE's A and B.Generally, the reductions were slightly faster in the microemulsion media than in the corresponding aqueous 2-propanol media.The significantly slower reduction of 4a relative to that of 3a in μE B indicated that the interphase is the reactive site.With enone 6a, the influence of microemulsions on the competition between 1,2- and 1,4-reduction was determined.In μE's A and B there was 8percent and 11percent 1,4-reduction, respectively, whereas in 2-PrOH A and B there was only a trace.With diketone 7a, the reactivity of the aromatic carbonyl group relative to that of the aliphatic carbonyl group increased on going from 2-PrOH A and B to μE's A and B, respectively.For the sodium borohydride reduction of ketones, microemulsion catalysis is more effective than phase transfer catalysis or the use of a tetraalkylammonium borohydride in a hydrocarbon solvent.